Electronic power module for a power tool having an integrated heat sink

ABSTRACT

An electronic switch module for a power tool having an electric motor is provided, including a printed circuit board (PCB), power switches mounted on the PCB and configured to switchably supply electric power from a power source to the electric motor, a series of primary heat sinks mounted on the PCB in association with the power switches, and a secondary heat sink mounted on the primary heat sinks and securely fastened to at least one of the primary heat sinks via a fastener, the secondary heat sink being electrically insulated from at least one of the primary heat sinks.

FIELD

This application relates to an electronic power module, and inparticular to an electronic power module in a power tool for driving abrushless DC motor.

BACKGROUND

Use of cordless power tools has increased dramatically in recent years.Cordless power tools provide the ease of a power assisted tool with theconvenience of cordless operation. Conventionally, cordless tools havebeen driven by Permanent Magnet (PM) brushed motors that receive DCpower from a battery assembly or converted AC power. In a PM brushedmotor, commutation is achieved mechanically via a commutator and a brushsystem. By contrast, in a brushless DC motor, commutation is achievedelectronically by controlling the flow of current to the statorwindings. A brushless DC motor includes a rotor for providing rotationalenergy and a stator for supplying a magnetic field that drives therotor. Comprising the rotor is a shaft supported by a bearing set oneach end and encircled by a permanent magnet (PM) that generates amagnetic field. The stator core mounts around the rotor maintaining anair-gap at all points except for the bearing set interface. Included inthe air-gap are sets of stator windings that are typically connected ineither a three-phase wye or Delta configuration. Each of the windings isoriented such that it lies parallel to the rotor shaft. Power devicessuch as MOSFETs are connected in series with each winding to enablepower to be selectively applied. When power is applied to a winding, theresulting current in the winding generates a magnetic field that couplesto the rotor. The magnetic field associated with the PM in the rotorassembly attempts to align itself with the stator generated magneticfield resulting in rotational movement of the rotor. A control circuitsequentially activates the individual stator coils so that the PMattached to the rotor continuously chases the advancing magnetic fieldgenerated by the stator windings. A set of sense magnets coupled to thePMs in the rotor assembly are sensed by a sensor, such as a Hall Effectsensor, to identify the current position of the rotor assembly. Propertiming of the commutation sequence is maintained by monitoring sensorsmounted on the rotor shaft or detecting magnetic field peaks or nullsassociated with the PM.

Conventionally, power switches are provided within the power tool inclose proximity to the motor or within the handle. Electronics includinga controller for controlling the power devices are also provided withinthe handle or in the vicinity of the motor. A trigger switch assembly isalso provided, preferable on the handle where it is easy for the user toengage. The controller is coupled to both the trigger assembly and thepower devices and regulates the flow of power through the power devicesbased on, for example, the travel distance of the trigger assembly.

The size and type of power devices may vary depending on the powerrequirements of the power tool. For low-voltage applications (e.g., 20VDC max), relatively small FETs that generate low heat may be suitable.However, as the tool voltage rating and/or power requirement increase,larger FETs or IGBTs, which generate considerably more heat, may beneeded. What is needed is an integrated power, control, and switchmodule that meets the heat dissipation requirements of these powerdevices.

This section provides background information related to the presentdisclosure and is not necessarily prior art.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

According to an aspect of the invention, an electronic switch module fora power tool having an electric motor is provided, including a printedcircuit board (PCB), power switches mounted on the PCB and configured toswitchably supply electric power from a power source to the electricmotor, a series of primary heat sinks mounted on the PCB in associationwith the power switches, and a secondary heat sink mounted on theprimary heat sinks and securely fastened to at least one of the primaryheat sinks via a fastener, the secondary heat sink being electricallyinsulated from at least one of the primary heat sinks.

In an embodiment, a module housing is provided within which the PCB isdisposed.

In an embodiment, a thermal pad is disposed between an upper portion ofthe primary heat sinks and a lower portion of the secondary heat sink toelectrically insulate the secondary heat sink from the primary heatsinks. In an embodiment, the thermal pad is made of thermally conductivematerial.

In an embodiment, an insulating frame is mounted over the secondary heatsink. In an embodiment, the insulating frame includes an insulating rimportion disposed to electrically insulate the fastener from thesecondary heat sink.

In an embodiment, motor wires are provided and end of the motor wiresare attached to the PCB to facilitate electrical connection with thepower switches. In an embodiment, the secondary heat sink includes aslot arranged to receive the motor wires therethrough.

In an embodiment, the secondary heat sink includes a main body and atleast one leg projecting downwardly from the main body, and theelectronic switch module includes at least one thermal pad strip made ofdeformable thermally-conductive and electrically-insulating materialdisposed between the leg of the secondary heat sink and the PCB.

In an embodiment, at least one metal body is disposed over the PCB forheat transfer from at least one of a circuit component mounted on thePCB or conductive track on the PCB. In an embodiment, the thermal padstrip is disposed between the metal body and the leg of the secondaryheat sink.

In an embodiment, a controller is disposed on the PCB, and an input unitcoupled to a trigger switch is also provided. In an embodiment, thecontroller is configured to control a switching operation of the powerswitches based on an input from the input unit.

In an embodiment, a power tool is provided including a housing, a motordisposed in the housing, and an electronic switch module coupled to themotor to control a supply of power to the motor. In an embodiment, theelectronic switch module may be provided with features described in thepreceding paragraphs.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present invention will become more fullyunderstood from the detailed description given herein below and theaccompanying drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusare not limitative of the example embodiments of the present invention.

FIG. 1 depicts a longitudinal cross-sectional view of a power tool witha housing half removed, according to an embodiment;

FIGS. 2A and 2B depict perspective views of an electronic control modulefrom two different angles, according to an embodiment;

FIGS. 3A and 3B respectively depict expanded front and back perspectiveviews of the electronic control module, according to an embodiment;

FIGS. 4A and 4B respectively depict a zoomed-in perspective view and across-sectional view of a the electronic control module showing thearrangement of a power switch and a heat sink on a printed circuit board(PCB), according to an embodiment;

FIG. 5 depicts a top view of the PCB, according to an embodiment;

FIG. 6 depicts an exemplary circuit diagram of power switches configuredas a three-phase inverter, according to an embodiment;

FIG. 7 depicts a perspective view of the electronic control moduleincluding a secondary heat sink, according to an additional and/oralternative embodiment;

FIG. 8 depicts a perspective view of the electronic control module ofFIG. 7 with module housing removed, according to an embodiment;

FIG. 9 depicts an exploded view of the electronic control module of FIG.8, according to an embodiment;

FIG. 10 depicts a partial zoomed-in cut-off view of the PCB andsecondary heat sink, according to an embodiment;

FIGS. 11 and 12 depict partial perspective views of the assembly stepsof the secondary heat sink, according to an embodiment;

FIG. 13 depicts a top view of a sense pad and conductive pads of theelectronic control module input unit, according to an embodiment; and

FIGS. 14 and 15 depict perspective zoomed-in views of the PCB with awiper moving over the sense pad and the conductive pads, according to anembodiment.

DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

With reference to the FIG. 1, a power tool 100 constructed in accordancewith the teachings of the present disclosure is illustrated in alongitudinal cross-section view. Power tool 100 in the particularexample provided may be a hand held impact driver, but it will beappreciated that the teachings of this disclosure is merely exemplaryand the power tool of this invention could be any power tool. The powertool shown in FIG. 1 may include a housing 102, an electric motor 104, abattery pack 108, a transmission assembly (gear case) 114, and an outputspindle 116. The gear case 114 may be removably coupled to the housing102. The housing 102 can define a motor housing 111 and a handle 112.

According to an embodiment, motor 104 is received in motor housing 111.Motor 104 may be be any type of motor and may be powered by anappropriate power source (electricity, pneumatic power, hydraulicpower). In an embodiment, the motor is a brushless DC electric motor andis powered by a battery pack 108.

According to an embodiment of the invention, power tool 100 furtherincludes an integrated electronic switch and control module 200(hereinafter referred to as “electronic control module”, or “controlmodule”). Electronic control module 200, in an embodiment, may include acontroller and electronic switching components for regulating the supplyof power from the battery pack 108 to motor 105. In an embodiment,electronic control module 200 is disposed within the handle 112 belowthe motor housing 111, though it must be understood that depend on thepower tool shape and specifications, electronic control module 200 maybe disposed at any location within the power tool. Electronic controlmodule may also integrally include components to support a user-actuatedinput unit 110 (hereinafter referred to as “input unit” 110) forreceiving user functions, such as an on/off signal, variable-speedsignal, and forward-reverse signal. In an embodiment, input unit 100 mayinclude a variable-speed trigger 120, although other input mechanismsuch as a touch-sensor, a capacitive-sensor, a speed dial, etc. may alsobe utilized. In an embodiment, an on/off signal is generated uponinitial actuation of the variable-speed trigger 120. In an embodiment, aforward/reverse button 122 is additionally provided on the tool 100. Theforward/reverse button 122 may be pressed on either side of the tool ina forward, locked, or reverse position. In an embodiment, the associatedcircuitry and components of the input unit 110 that support thevariable-speed trigger 120 and the forward/reverse button 122 may befully or at least partially integrated into the electronic controlmodule 200. Based on the input signals from the input unit 110 andassociated components, the controller and electronic switchingcomponents of the electronic control module 200 modulate and regulatethe supply of power from the battery pack 108 to motor 105. Details ofthe electronic control module 200 are discussed later in detail.

While in this embodiment, the power source is battery pack 108, it isenvisioned that the teachings of this disclosures may be applied to apower tool with an AC power source. Such a power tool may include, forexample, a rectifier circuit coupled to the AC power source.

It must be understood that, while FIG. 1 illustrates a power tool impactdriver having a brushless motor, the teachings of this disclosure may beused in any power tool, including, but not limited to, drills, saws,nailers, fasteners, impact wrenches, grinders, sanders, cutters, etc.Also, teachings of this disclosure may be used in any other type of toolor product that include a rotary electric motor, including, but notlimited to, mowers, string trimmers, vacuums, blowers, sweepers, edgers,etc.

The electronic control module 200 is described herein, according to anembodiment of the invention. FIGS. 2A and 2B depict perspective views ofelectronic control module 200 from two different angles, according to anembodiment. FIGS. 3A and 3B depict exploded front and back views of thesame module 200, according to an embodiment. Reference is made to thesedrawings herein.

Electronic control module 200, in an embodiment, includes a printedcircuit board (PCB) 202 arranged and mounted inside a module housing204. Module housing 204 includes a bottom surface 227, side walls 228,and an open face. PCB 202 is inserted through the open face and securedinside the module housing 204. Side walls 228 include retention features229 for securely holding the PCB 202 at a distance from the bottomsurface 227. Control module 200 includes two compartments—an enclosedcompartment 210 a that houses and encloses a first part of the PCB 202and components associated with the input unit 110, as described below,and an open compartment 210 b, and partially encloses a second part ofthe PCB 202. Within the open compartment 210 b, module housing 204encloses the lower surface and the sides of PCB 202, but leaves theupper surface of the PCB 202 substantially exposed. Mounted on the uppersurface of PCB 202 are a series of power switches 206 and a series ofheat sinks disposed over the power switches 206 and secured to the PCB202. As discussed below in detail, this arrangement allows cooling airto transfer heat away from the heat sinks 208 within the power tool 100,but protects the input unit 110 components from any dust and debris fromthe cooling air.

According to an embodiment, control module 200 includes a controller218. In an embodiment, the controller may be mounted to a lower surfaceof the PCB 202 and be in electronic communication with the rest of thePCB 202 components through vias (not shown). In an embodiment,controller 218 may be a programmable micro-controller, micro-processor,or other processing unit capable of controlling the motor and variousaspects of power tool. For example, controller 218 may be programmed toturn on and off power switches 206, as discussed below, to controlcommutation of the brushless motor. In an embodiment, controller 218 maybe coupled to a series of gate drivers disposed on the PCB 202, which inturn are connected to the gates of the power switches 206.Alternatively, controller 218 may be a circuit chip that includes both amicro-controller and the gate drivers and be coupled directly to thegates of the power switches 206. Using the gate drivers, controller 218turns the power switches 206 on or off selectively to commutate themotor and control the speed of the motor. Additionally, the controllermay be programmed to various tool and battery pack operation features,such as tool and/or temperature control, battery pack voltage control,and tool over-current detection and control, etc. In an alternativeembodiment, the controller may be an Application Specific IntegratedCircuit (ASIC) configured to control the aforementioned aspects of themotor, battery, and power tool.

In an exemplary embodiment, power switches 206 may be Field EffectTransistors (FETs). In an embodiment, six power switches 206, includingthree high-side power switches and three low-side power switches, arearranged and coupled together as a three-phase bridge rectifier circuit.Using the gate drivers, controller 218 sequentially turns the powerswitches 206 on and off within each phase of the brush motor 104commutation. Further, the controller 218 performs pulse-width modulation(PWM) of the power switches 206 within each phase to regulate the speedof the motor based on speed signals received from input unit 110, asdescribed below. Controller 218 further controls the direction of motorcommutation based on a forward/reverse signal received from input unit110, also discussed below.

It is noted that while the power switches 206 discussed herein are FETs,other types of power switches such as BJTs or IGBTs may be utilized.Additionally, while power switches 206 are arranged as a three-phasebridge rectifier for driving a three-phase brushless motor, other numberand arrangement of power switches may be used to drive other types ofmotors, including brushed or brushless motors.

As described above, module housing 204 leaves the upper surface of thePCB 202 exposed, thus allowing heat to dissipate from the heat sinks208. Electronic control module 200 may be placed within a path of airflow inside the power tool, e.g., inside the power tool handle 112 influid communication with motor fan 106 so that airflow generated bymotor fan 106 runs through the handle 112. The air flow generated withinthe handle further improves heat dissipation from the electronic controlmodule 200.

In an embodiment, the PCB 202 is further potted with a layer of pottingcompound (not shown) in the open compartment 210 b. The layer of pottingcompound, in an embodiment, substantially covers most of the circuitcomponents on the PCB, but leave a top plate of heat sinks 206 exposedso the heat sinks 208 can dissipate heat away from the power switches206. While the potting compound is not shown in FIGS. 2A-3B, the controlmodule of FIG. 1 is shows with the potting compound disposed inside thehousing 202.

FIGS. 4A and 4B depict zoomed-in perspective and cross-sectional viewsof PCB 202, showing the arrangement of heat sink 208 and power switch206 (in this case a FET) mounted over PCB 202, according to anembodiment. Heat sink 208 includes two legs mounted on the PCB 202. Themain plate of heat sink 208 is located directly above power switch 206at close proximity thereto. This allows heat to be transferred directlyfrom power switch 206 to the heat sink 208 through a small air gapbetween the two. In an embodiment, the main plate of the heat sink 208has a surface area of 10 to 40 mm², preferably 15-35 mm², morepreferably 20-30 mm², that is exposed after the potting compound isapplied. In addition, one or more of the legs of the heat sink 208 iselectrically connected to the drain of power switch 206 on the PCB 202.This arrangement further improves heat transfer from the FET 206 to theheat sink 208.

It is noted that while in this embodiment discrete heat sinks 208 aremounted on respective power switches 206, a lower number of heat sinks208 may be utilized instead. In an alternative embodiment of theinvention, a single heat sink is mounted on the PCB over the powerswitches 206 to provide a higher surface area for heat transfer.

Referring back to FIGS. 2A through 3B, in an embodiment, a series ofoutput wires 212 are secured on one end to a surface of the PCB 202.These wires connect the outputs of the power switches three-phase bridgerectifier to the power terminals the brushless motor 104. In anembodiment, a series of control signal wires 214 are also secured to awire receptacle 215 a. In an embodiment, wire receptacle 215 a ismounted on the PCB and is in electrical communication with thecontroller 218. The control signal wires 214 allow the controller 218 tocommunicate with other parts of the power tool 100, such as the motor104 and the battery 108. In an embodiment, hall signals from thebrushless motor hall sensors communicate with the controller 218 throughthese control signal wires 214. Control signal wires 214 mayadditionally be provided with a control terminal 215 b to ease plug-inconnectivity of external wires with the control signal wires 214. In anembodiment, a pair of power input wires 217 are also secured on thesurface of PCB 202. These wires are coupled to a power source (e.g.,battery 108) via a power terminal 216 to supply power from the powersource to the power switches 206.

In an embodiment, control module 200 includes an encapsulation member260 that mates with the module housing 204 to form the enclosedcompartment 210 a of control module 200. As discussed below in detail,encapsulation member 260 protects components associated with input unit110 from dust and debris. Encapsulation member 260 also includes wireretaining features 262 and wire guide features 264 for retaining andpositioning signal wires 214 and/or power output wires 212 away from thehousing 204. Encapsulation member 260 further includes mating features266 that mate with corresponding mating features 268 on the modulehousing 204. In an embodiment, the mating features 268 include lips thatsnap fit into slots in mating features 266. In an embodiment,encapsulation member 260 further includes an opening 269 that allowscontrol signal wires 214 to connect to PCB-side control terminal 215 a.

Additionally, in an embodiment, control module 200 includes anadditional cover 270 that covers a lower portion of PCB 202. Cover 270also includes wire retaining features 272 for retaining the power wires217, as well as wire guide features 274 for guiding the wires 217 aroundcircuit components (e.g., capacitors 280) mounted on PCB 202. Cover 270further includes mating features 276 that mate with corresponding matingfeatures 278 on the module housing 204. In an embodiment, the matingfeatures 278 include lips that snap-fit into slots in mating features276.

In an embodiment, control module 200 is additionally provided with anauxiliary control terminal 252 mounted on a top portion of the PCB 202that allows the controller 218 with other motor or tool components. Inan embodiment, auxiliary control terminal 252 allows the controller 218to communicate with an LED provided on the tool 100. In an embodiment,auxiliary control terminal 252 is provided outside and adjacent to theenclosed compartment 210 a.

The input unit 110 is discussed herein, according to an embodiment ofthe invention. According to an embodiment, input unit 110 is at leastpartially integrated into control module 200. In an embodiment, inputunit 110 incorporates electro-mechanical elements for variable-speeddetection, on/off detection, and forward/reverse detection inside theenclosed compartment 210 a of control module 200, as discussed herein.

In an embodiment, input unit 110 includes a forward/reverse actuator 220supported by the enclosed compartment 210 a portion of the modulehousing 204. In an embodiment, forward/reverse actuator 220 includes acontact member 220 a, which holds an electrical connector 222 and isdisposed inside the enclosed compartment 210 a of the module housing204, and an engagement member 220 b, which is located outside the modulehousing 204. In an embodiment, engagement member 220 b is in movingcontact with forward/reverse button 122 on the power tool 100. A pivotmember 220 c located between the contact member 220 a and engagementmember 220 b is supported by the module housing 204 and provides a pivotpoint for the forward/reverse actuator. A biasing member 224 is securedto the module housing 204 to engage and bias the contact member 220 a ina forward, neutral (e.g., locked), or reverse direction. In anembodiment, biasing member 224 is secured in an opening of a holder,i.e. a post 226 that projects from the bottom surface 227 of the modulehousing 204 within the enclosed compartment 210 a. In an embodiment, PCB202 is provided with a through-hole 254 that receives the post 226. Whenthe user presses the forward/reverse button 122 from either side of thetool to a forward, locked, or reverse position, the forward/reversebutton 122 moves the engagement member 220 around the pivot portion 220c. Pivoting movement of the engagement member 220 b around the pivotportion 220 c causes the electrical connector 222 of contact member 220a to make or break contact with a contact-sensing member against thebiasing force of the biasing member 224. In an embodiment, contact sensemember includes a pair of conductive tracks 250 arranged on PCB 202.

In an embodiment, one of the conductive tracks 250 is electricallyconnected to power source 108 and the other is connected to and sensedby controller 218. Voltage is present and sensed by the controller 218when electrical connector 222 makes contact with the pair of conductivetracks 250, thus electrically connecting the two conductive tracks 250.Presence or lack of sensed voltage is indicative of whether the motorshould rotate in the forward or reverse direction. Functional details ofuse and electrical connectivity of conductive tracks 250 forforward/reserve detection are discuss in U.S. Pat. No. 9,508,498 filedMay 21, 2012, which is incorporated herein by reference in its entirety.

According to an embodiment, input unit 110 further includes avariable-speed actuator 230. Variable-speed actuator includes a linkmember 232 that extends out of the module housing 204 from a slidingmember 234 that is arranged inside the module housing 204 and supports aconductive wiper 236. Link member 232 is coupled to trigger 120 that isengageable by the user. The sliding member 234 supports and engages acompression spring 238 its longitudinal end opposite link member 232.Compression spring 238 is located between an inner wall of the modulehousing 204 and the sliding member 234. When the user presses thetrigger 120, the sliding member 234 moves against a biasing force of thespring 238.

Conductive wiper 236 contacts a speed-sensing member located on thesurface of the PCB 202. In an embodiment, the speed-sensing member is aseries of variable-speed conductive tracks 240 arranged on the PCB 202.Actuation of the trigger 120 moves the conductive wiper 236 over theconductive tracks 240. Initial movement of the conductive wiper 236 overthe conductive tracks 240 generates a signal that turns controller 218ON. Additionally, an analog variable-voltage signal is generated basedon the movement of the conductive wiper 128 over the conductive tracksand that signal is sent to the micro-controller. This signal isindicative of the desired motor speed. Functional details of ON/OFF andvariable-speed detection using conductive tracks 240 are discuss in U.S.Pat. No. 9,508,498 filed May 21, 2012, which is incorporated herein byreference in its entirety. It must be understood, however, that anyknown variable-voltage speed-sensing mechanism, such as a resistivetape, may be a utilized within the scope of the invention.

It is noted that the moving mechanical parts of the forward/reverseactuator 220 and variable-speed actuator 230 (including the electricalconnector 222 and conductive wiper 236), alone or in combination withconductive tracks 240 and 250, are referred to in this disclosure as“electro-mechanical” elements.

FIG. 5 depicts a top view of PCB 202 alone without any componentsmounted. As shown herein, PCB 202 is provided with metal traces 282 formounting the power switches 206, as well as variable-speed conductivetracks 240 and forward/reverse conductive 250. Through-hole 254 andauxiliary terminal 252 is also shown in this figure.

In an embodiment, a layer of silicon conformal coating is applied to thePCB 202 to protect it from dust, debris, moisture, and extremetemperature changes. However, since the conductive tracks 250 and 240need to remain exposed to make electrical contact with theforward/reverse electrical connector 222 and variable-speed conductivewiper 236, a high temperature resistant tape 284 is applied to the PCB202 over the conductive tracks 240 and 250 before the silicon conformalcoating is applied. The high temperature resistant tape 284 ensures thatthe silicon conformal coating does not cover the conductive tracks 240and 250.

FIG. 6 depicts an exemplary circuit diagram of the power switches 206configured as a three-phase inverter bridge circuit, according to anembodiment. As shown herein, the three-phase inverter bridge circuitincludes three high-side and three low-side switches 206. The gates ofthe high-side power switches are driven via drive signals UH, VH, andWH, and the gates of the low-side power switches are driven via drivesignals UL, VL, and WL. In an embodiment, these signals are coupled to agate driver circuit controlled by the controller 218. In an embodiment,the drains of the high-side power switches are commonly coupled to theDC+ terminal of the power supply. Thus, the drains of the high-sidepower switches have the same electrical potential. Similarly, thesources of the low-side power switches are commonly coupled to theDC-terminal of the power supply and have the same electrical potential.The sources of the high-side switches are respectively coupled to thedrains of the corresponding low-side power switches to output powersignals PU, PV, and PW. These output power signals are coupled via wires212 to motor terminals for driving the phases of the motor.

An additional and/or alternative embodiment of the invention isdescribed herein with reference to FIGS. 7-12.

FIG. 7 depicts a perspective view of the electronic control module 200,additionally provided with a secondary heat sink 310 and an insulatingframe 320, for improved heat transfer from the power switches 206,according to an embodiment. FIG. 8 depicts a perspective view of theelectronic control module 200 of FIG. 7, with the module housing 204removed to show the PCB 202 and the associated components. FIG. 9depicts an exploded perspective view of FIG. 8, according to anembodiment.

As shown in these figures, similarly to embodiment of FIGS. 2A-5, thepower switches 206 of the electronic control module 200 are providedwith a series of discrete heat sinks, herein referred to as primary heatsinks 302 a-f, surface-mounted on the PCB 202. In this embodiment,primary heat sinks 302 a-c are mounted in association with the high-sidepower switches and primary heat sinks 302 d-f are mounted in associationwith the low-side power switches. As previously described, each primaryheat sink 302 a-f includes a main plate placed above a correspondingpower switch 206, with legs that are surface mounted on the PCB 202 onboth sides of the corresponding power switch 206. In an embodiment, atleast one of the legs of the primary heat sinks 302 a-f is electricallycoupled to the drain of the corresponding power switch 206 for improvedheat transfer.

It must be understood that while in this embodiment, the power switches206 are mounted on the top surface of the PCB 202 opposite thecontroller 218, the power switches 206 may alternatively be mounted onthe bottom surface of the PCB 202 opposite the primary heat sinks 302a-f. In such a construction, the main body of each of the primary heatsinks 302 a-f may be fully mounted on the top surface of the PCB 202opposite the corresponding power switch 206 and electrically connectedto the drains of the corresponding power switch 206 through the PCB 202.

In an embodiment, depending on the power tool voltage rating and powerout requirements, the primary heat sinks 302 a-f may not sufficientlydissipate heat away from the power switches 202, leading to rapidtemperature increases when used continuously in high load/high loadcondition. To overcome this problem, according to an embodiment,secondary heat sink 310 and insulating frame 320 are provided asdescribed herein.

In an embodiment, secondary heat sink 310 includes a main body mounteddirectly over the top surface of the primary heat sinks 302 a-f, and oneor more legs 314 projecting downwardly from the min body. Secondary heatsink 310 is provided with one or more through-holes (in this example twothrough-holes 316 on opposite corners) that receive fastening pins 340for attachment to one or more of the primary heat sinks (in this exampleone high-side switch 302 c and one low-side switch 302 d). In anembodiment, high-side primary heat sink 302 c and low-side primary heatsink 302 d are each provided with a corresponding threaded fasteningreceptacle 306 that receive the fastening pins 340 through thethrough-holes 316 of the primary heat sink 310. Threaded fasteningreceptacles 306 may be provided as a threaded through-holes drilled andthreaded into the primary heat sinks 302 c and 302 d. Alternatively,fastening receptacles 306 may be provided as separate threaded insertspressed into holes on the primary sinks 302 c and 302 d. Witharrangement the secondary heat sink 310 is secured directly to one ormore of the primary heat sinks 302 a-f, rather than, for example, themodule housing 204. This arrangement substantially eliminates orsignificantly reduces any air gap between the primary heat sinks 302 a-fand the secondary heat sink 310, thus significantly improving betterheat transfer between the primary heat sinks 302 a-f and the secondaryheat sink 310.

In an embodiment, secondary heat 310 sink further includes an elongatedslot 318 arranged for passage of the power output wires 212 coming outof the PCB 202.

In an embodiment, a thermal pad 330 is disposed on the lower portion ofthe secondary heat sink 310 between the secondary heat sink 310 and theprimary heat sinks 302 a-f. Thermal pad 330 is made of a thin layer ofelectrically-insulating, thermally-conductive material that allow heatto transfer from the primary heat sinks 302 a-f to the secondary heatsink 310, but electrically insulates the secondary heat sink 310 fromall the primary heat sinks 302 a-f. In an embodiment, thermal pad 330 isprovided with through-holes 336 and an elongated slot 338 shapedrespectively like through-holes 316 and elongated slot 318 of thesecondary heat sink 310.

In an embodiment, insulating frame 320 is provided for more effectivemounting and additional insulation of the secondary heat sink 320. In anembodiment, insulating frame 320 includes two through-holes 326 forreceiving the fastening pins 340, and circular downwardly-projectingrims 324 arranged to be received within the through-holes 316 of thesecondary heat sink 310. Rims 324 circumferentially separate andelectrically insulate the fastening pins 340 from the secondary heatsink 310.

In an embodiment, fastening pins 340 are fastened (and thus electricallycoupled) to primary heat sinks 302 c and 302 d, which are in turnelectrically coupled to the drains of their corresponding power switches206. Fastening pins 340 are therefore coupled to two differentelectrical potentials. The rims 324 of the insulating frame 320electrically insulate the secondary heat sink 310 from the fasteningpins 340 along the insertion axis of the fastening pins 340, thusensuring that the secondary heat sink 320 is not electrically coupled toany of the power switches 206.

In an embodiment, insulating frame 320 is also provided with anelongated slot 328 for passage of the power output wires 212. In anembodiment, insulting frame 320 also includes downwardly-projectingwalls formed around the elongated slot 328 to separate the power outputwires 212 from the edges of the secondary heat sink 310 around theelongated slot 318, which may cut into and damaging to the wires 212.

In an embodiment, the insulating frame 320 further includes a wireretaining portion 322 having a substantially U-shaped profile thatguides and retains the power output wires 212 coming through theelongated slot 328.

In an embodiment, one or more strips of thermal pads 360, 362 made ofelectrically-insulating and thermally-conductive material may bedisposed between the legs 314 of the secondary heat sink 310 and thesurface of the PCB 202. In an embodiment, thermal pad strips 360 and 362may be disposed directly over the upper surface of the PCB 202, or overmetal bodies 350. Metal bodies 350 are heat-carrying elements such ascopper slugs positioned strategically on conductive tracks of the PCB202 that carry high current, or near circuit components (e.g., fuses)that generate significant heat. In an embodiment, thermal pad strips360, 362 may be made of flexible material that deform around metalbodies 350 and/or aforementioned circuit components as they are presseddown. In this manner, thermal pad strips 360, 362 cover the edges andside walls metal bodies 350 to ensure that the metal bodies 350 arefully insulated from the secondary heat sink 310, even in high debrisenvironments where metal particles may get struck around the secondaryheat sink 310. In addition, the elasticity of the thermal pad strips360, 362 accounts for dimentional tolerances associated with thesecondary heat sink 310 and other components.

As discussed above with reference to FIG. 6, the drains of the low-sidepower switches 206, which are electrically coupled to primary heat sinks302 d-f, are at different electrical potentials. Thus, if the electriccontrol module 200 is contaminated with metal particles in the area ofthe primary heat sinks 302 d-f and two of the adjacent primary heatsinks 302 d-f are shorted together, it could result in catastrophicsystem failure. To ensure that the primary heat sinks 302 d-f areinsulated from one another in the event of such contamination, accordingto an embodiment, a rectangular-shaped insulating member 308 is disposedaround the middle primary heat sink 302 e on the PCB 202. The insulatingmember 308 has substantially the same height as the primary heat sink302 e and extends from the surface of the PCB 202 to the thermal pad330.

FIG. 10 depicts a zoomed-in perspective cross-view of the secondary heatsink 310 mounted on the PCB 202 and secured to the primary heat sink 302c, according to an embodiment. As shown herein, the circulardownwardly-projecting rims 324 of the insulating frame 320circumferentially insulates and separates the fastening pin 340 from thesecondary heat sink 310. Fastening receptacle 306 of the primary heatsink 302 c is threaded and interfaces with the threaded portion of thefastening pin 340. As the fastening pin 340 is fastened, the leg 314 ofthe secondary heat sink presses on the thermal strip 360, which deformsaround the metal body 350 until it comes in contact with, or comessubstantially close to, the surface of the PCB 202.

The use of the secondary heat sink 310 as described in this embodimentallows the electronic control module 200 to be used in higherpower/higher current power tool applications while effectively managingthe temperature of the power switches 206. It was, for example, that thesecondary heat sink 310 increases the steady-state capability of theelectronic control module 200 in continuous use from under 40 amps toapproximately 70 amps while keeping the temperature of the powerswitches 206 and other module 200 components at under 120 Celsius.

FIGS. 11 and 12 depict partial prospective views of the electroniccontrol module 200 during the assembly process, according to anembodiment. As shown in FIG. 11, in an embodiment, thermal pad strips360 and 362 are initially placed over the PCB 202 and/or the metalbodies 350. Thermal pad 330 (not shown) is also securely placed on alower surface of the secondary heat sink 310. The insulating member 308is disposed around the middle low-side primary heat sink 302 e. Then, asshown in FIG. 12, the secondary heat sink 310 is mounted over theprimary heat sinks 302 a-f, with the legs 314 placed over the thermalpad strips 360 and 362. The insulating frame 320 is then positioned ontop of the secondary heat sink 310 and the fasteners 340 located withinthe through-holes 326 to fasten the enter assembly to the primary heatsinks 302 c and 302 d.

Another aspect/embodiment of the invention is described herein withreference to FIGS. 13-15.

As described above with reference to FIGS. 3A and 3B, input unit 110 ofthe electronic control module 200 includes variable-speed actuator 230,which includes sliding member 234 supporting conductive wiper 236. Whenthe user presses the trigger 120, the sliding member 234 moves against abiasing force of spring 238, and conductive wiper 236 makes slidinglycontact with speed-sensing member located on the surface of the PCB 202.In an embodiment, the speed-sensing member is a series of variable-speedconductive tracks 240 arranged on the PCB 202, an actuation of thetrigger 120 moves the conductive wiper 236 over the conductive tracks240. Initial movement of the conductive wiper 236 over the conductivetracks 240 generates a signal that turns controller 218 ON.Additionally, an analog variable-voltage signal is generated based onthe movement of the conductive wiper 128 over the conductive tracks andthat signal is sent to the micro-controller.

U.S. Pat. No. 9,508,498 filed May 21, 2012, which is incorporated hereinby reference in its entirety, described the arrangement and circuitconnectivity of the variable speed conductive tracks 240 in detail (seeFIGS. 10A-13C). As described in this disclosure, the conductive tracks240 include a sense pad 160 and a series of conductive tracks 162arranged in line with the sense pad 160. At its initial defaultposition, the wiper 128 makes contact with pad 162(20), which is coupledto the B+ terminal of the power supply. As the trigger is pressed, thewiper moves from pad 162(20) to pad 162(19), causing a large voltagedrop to be sensed on sense pad 160, which generates a signal to beginsupplying power to the controller. From there, as the trigger is pressedfurther, the wiper moves from pad 162(19) all the way to pad 162(1) atits fully-pressed position, resulting in stepped voltage drop on thesense pad 160. The controller monitors the voltage on the sense pad 160and controls the speed of the motor according to the voltage level onthe sense pad 160.

The tips of the wiper (See e.g., tips a-d of the wiper 128 in FIG. 10Aof the '498 patent) are often chamfered for smooth movement of the wiperover the conductive pads. However, due to manufacturing process orequipment failure, the wiper tips of some wipers may inadvertentlyinclude sharp edges capable of cutting into the conductive tracks andscraping off strips of metal that then get stuck between adjacentconductive pads. This is particularly problematic if the sharp edges ofthe wiper cut into the sense pad or the two end pads, where the traveldistance of the wiper edge may be up to 10 mm. These metal strips mayget struck between the conductive tracks and cause serious systemfailure—e.g. between sense pad 160 and end pad 162(20) in the '498patent, in which case the tool will not turn on with trigger pull, orbetween the end pad 162(20) and resistive pad 162(19), in which case thetool will turn on inadvertently.

In order to overcome this problem, according to an embodiment of theinvention, a segmented pad design is provided, as shown in FIGS. 13-15.FIG. 13 depicts a top view of the sense pad 460 and conductive pads 462.FIGS. 14 and 15 depict perspective zoomed-in views of the PCB 202 withthe wiper 236 moving over the sense pad 460 and the conductive pads 462.

As shown in these figures, sense pad 460 is partitioned into a series ofsegments 470 disposed on the PCB 202 with parallel linear gaps 472therebetween. In other words, sense pad 460 is printed on the PCB 202with linear gaps 472 so as to expose the PCB 202 between segments 470.The end pads 462(1) and 462(20) of the conductive pads 462 may similarlybe segmented into a series of segments 470 with linear gaps 472therebetween.

In an embodiment, the linear gaps 472 may be oriented diagonally withrespect to an axis of movement of the wiper 236. Alternatively, lineargaps 427 may be disposed substantially perpendicularly with respect tothe axis.

In an embodiment, linear gaps 427 extend from axial boundary portions474 so as to intersect the travel path of the wiper 236 tips. As such,the boundary portions 474 electrically connect the segments 470together.

In an embodiment, linear gaps 427 are positioned such that a width ‘C’of each segment 470 along the axis of movement of the wiper 236 issmaller than distance ‘A’ between the sense pad 460 and the end pad462(20). In an embodiment, distance ‘C’ is also smaller than distance‘B’ between end pad 462(20) and the nearest conductive pad 462(19). Thisconfiguration ensures that as the wiper 236 moves along the sense pad460 and/or the conductive pads 462, it cannot scrape off a strip ofmetal debris longer than the distances ‘A’ or ‘B’. In other words, evenif a piece of the sense pad 460 or the conductive pads 462 is scrapedoff by the wiper 236 edges, the length of the piece cannot be largeenough to electrically short the sense pad 460 to the end pad 462(20),or the end pad 462(20) to the conductive pad 462(19).

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

1. An electronic switch module for a power tool having an electricmotor, comprising: a printed circuit board (PCB); a plurality of powerswitches mounted on the PCB and configured to switchably supply electricpower from a power source to the electric motor; a plurality of primaryheat sinks mounted on the PCB in association with the plurality of powerswitches; and a secondary heat sink mounted on the plurality of primaryheat sinks and securely fastened to at least one of the plurality ofprimary heat sinks via a fastener, the secondary heat sink beingelectrically insulated from at least one of the plurality of primaryheat sinks.
 2. The electronic switch module of claim 1, furthercomprising a module housing within which the PCB is disposed.
 3. Theelectronic switch module of claim 1, further comprising a thermal paddisposed between an upper portion of the plurality of primary heat sinksand a lower portion of the secondary heat sink to electrically insulatethe secondary heat sink from the plurality of primary heat sinks, thethermal pad comprising thermally conductive material.
 4. The electronicswitch module of claim 1, further comprising an insulating frame mountedover the secondary heat sink, the insulating frame comprising aninsulating rim portion disposed to electrically insulate the fastenerfrom the secondary heat sink.
 5. The electronic switch module of claim1, further comprising a plurality of motor wires ends of which areattached to the PCB to facilitate electrical connection with theplurality of power switches, the secondary heat sink comprises a slotarranged to receive the plurality of motor wires therethrough.
 6. Theelectronic switch module of claim 1, wherein the secondary heat sinkcomprises a main body and at least one leg projecting downwardly fromthe main body, and the electronic switch module comprises at least onethermal pad strip comprising deformable thermally-conductive andelectrically-insulating material disposed between the leg of thesecondary heat sink and the PCB.
 7. The electronics switch module ofclaim 6, further comprising at least one metal body disposed over thePCB for heat transfer from at least one of a circuit component mountedon the PCB or conductive track on the PCB, wherein the at least onethermal pad strip is disposed between the at least one metal body andthe leg of the secondary heat sink.
 8. The electronic switch module ofclaim 1, further comprising a controller disposed on the PCB, and aninput unit coupled to a trigger switch, wherein the controller isconfigured to control a switching operation of the plurality of powerswitches based on an input from the input unit.
 9. A power toolcomprising: a housing; a motor disposed in the housing; and anelectronic switch module coupled to the motor to control a supply ofpower to the motor, the electronic switch module comprising: a printedcircuit board (PCB); a plurality of power switches mounted on the PCBand configured to switchably supply electric power from a power sourceto the electric motor; a plurality of primary heat sinks mounted on thePCB in association with the plurality of power switches; a secondaryheat sink mounted on the plurality of primary heat sinks and fastened toat least one of the plurality of primary heat sinks via a fastener, thesecondary heat sink being electrically insulated from at least one ofthe plurality of primary heat sinks.
 10. The power tool of claim 9,further comprising a module housing within which the PCB is disposed.11. The power tool of claim 9, further comprising a thermal pad disposedbetween an upper portion of the plurality of primary heat sinks and alower portion of the secondary heat sink to electrically insulate thesecondary heat sink from the plurality of primary heat sinks, thethermal pad comprising thermally conductive material.
 12. The power toolof claim 9, further comprising an insulating frame mounted over thesecondary heat sink, the insulating frame comprising an insulating rimportion disposed to electrically insulate the fastener from thesecondary heat sink.
 13. The power tool of claim 9, further comprising aplurality of motor wires ends of which are attached to the PCB tofacilitate electrical connection with the plurality of power switches,the secondary heat sink comprises a slot arranged to receive theplurality of motor wires therethrough.
 14. The power tool of claim 9,wherein the secondary heat sink comprises a main body and at least oneleg projecting downwardly from the main body, and the electronic switchmodule comprises at least one thermal pad strip comprising deformablethermally-conductive and electrically-insulating material disposedbetween the leg of the secondary heat sink and the PCB.
 15. The powertool of claim 14, further comprising at least one metal body disposedover the PCB for heat transfer from at least one of a circuit componentmounted on the PCB or conductive track on the PCB, wherein the at leastone thermal pad strip is disposed between the at least one metal bodyand the leg of the secondary heat sink.